Color photodetector arrays, such as color photodetector arrays used in digital cameras, utilize an array of photodiodes or other type of photodetector to record an image. Each photodiode is typically a broad-band detector, that is, the photodiode responds to some degree to all the visible colors, and also to infrared (“IR”) light, which is not visible.
To provide color sensitivity, the photodetectors are typically divided into three classes of photodetectors that detect red, green, or blue light. Red, green, and blue transmissive color filters are typically applied to a photodetector array in a particular pattern to provide the red, green, and blue photodetectors. One technique is to apply a small dot of dye having the desired color (e.g. red, green, or blue dye) over each photodetector. However, the dyes that are used to provide color selectivity in the color photodetector array do not effectively block IR light, and an IR filter is incorporated into the color photodetector array. Without an IR blocking filter, ambient IR light could cause overexposure or an exposure error, such as saturation of the photodetector, or incorrect color rendering, such as by causing red photodetectors to register an inaccurately high level of red light.
One approach to providing an IR filter in a color photodetector array device is to attach a piece of glass commonly known as “IR glass,” which is formulated to absorb IR light, over the photodetector array. Unfortunately, IR glass is relatively expensive and thick. The thickness increases the height of a packaged device and results in an undesirably heavy assembly that is prone to cracking. Another approach is to attach a thin-film IR filter fabricated on a thin (about 1 mm) glass substrate over the photodetector array. Even an IR filter this thin undesirably increases the package thickness. Thin film filters, while readily available, increase packaging cost. The filter attachment process is relatively slow (in units per hour) and creates a potential for a manufacturing bottleneck, and a tight process control is important for proper filter placement.
Therefore, an improved technique for providing IR filtering with a photodetector array is desirable.